This project will continue studying the relationship of the HLA genetic system to possible human immune response genes and disease susceptibility. Specific diseases will be examined for HLA antigen frequency disturbances. Of particular interest is the determination of HLA-DR specificities in disease patients, since these antigens seem to be analogous to immune response related genetic regions in other mammalian species. Considerable effort will be made to understand the mechanisms of the transfusion effect in human homograft survival. This effect has been clearly shown to be the overwhelmingly dominant factor in graft survival, and further study of the immunologic basis is critical to understanding this phenomenon.